//To avoid reaching the write speed capacity of the hard disk, limit all writes

#include <stdbool.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include "errorAndExit.h"
#include "rateLimiter.h"
#include "utils/min.h"

//How many bytes we can write to disk per second. Use 0 to specify no limit. Default is 30 MB/s.
unsigned long diskSpeed = 30UL * 1024UL * 1024UL;
/** If we are not writing to disk, how many seconds the capacity can keep increasing before it reaches the limit.
 * Increasing this value can result in a spike of data once we are writing to disk again, but then allows the data
 * to quickly be written without having to wait for capacity to be available. */
#define MAX_IDLE_TIME 3UL
//Capacity can be filled up to this maximum amount
#define CAPACITY_MAX diskSpeed * MAX_IDLE_TIME

//The current amount of free capacity
unsigned long capacity = 0UL;

time_t prevTime = 0;

/** Set disk speed to the given speed in bytes per second. */
void setDiskSpeed(unsigned long newSpeed) {
  diskSpeed = newSpeed;
}

/** Increases the capacity based on time elapsed since the last time this function was called */
void increaseCapacity() {
  //Get seconds since the last time this function was called, or default to 1 if this is the first time this function is called
  unsigned long timeElapsed = 1;
  if (prevTime == 0) {
    time(&prevTime);
  } else {
    time_t prevTimeCache = prevTime;
    time(&prevTime);
    timeElapsed = prevTime - prevTimeCache;
  }

  capacity = min(CAPACITY_MAX, capacity + timeElapsed * diskSpeed);
}

/** Pauses execution until the given amount of capacity is available */
void consumeCapacity(unsigned long numBytes) {
  //Exit early if there is no capacity limit
  if (CAPACITY_MAX == 0UL) {
    return;
  }

  if (numBytes > CAPACITY_MAX) {
    fprintf(stderr, "Could not consume %lu bytes in rate limiter; maximum is %lu.\n", numBytes, CAPACITY_MAX);
    errorAndExit();
  }

  increaseCapacity();

  //While not enough capacity is available
  while (capacity < numBytes) {
    //Sleep for one second
    sleep(1U);
    increaseCapacity();
  }

  //Consume capacity
  capacity -= numBytes;
}